Mechanical disturbances can be used to establish acoustic waves in earth formations surrounding a borehole, and the properties of these waves can be measured to obtain information about the formations through which the waves have propagated. Parameters of compressional, shear and Stoneley waves, such as their velocity (or its reciprocal, slowness) in the formation and in the borehole, can be indicators of formation characteristics that help in evaluation of the location and/or producibility of hydrocarbon or other resources.
Typically, a logging tool is run into the borehole, where the logging tool includes one or more sonic (acoustic) sources (transmitters) and multiple spaced apart receivers. Measurements are made by the receivers as the logging tool is moved slowly in the borehole. The sonic signals from the one or more transmitters enter the formation adjacent the borehole, and the arrival times and possibly other characteristics of receiver responses are used to find formation parameters.
Conventionally, shear wave signals (S-waves) detected by the receivers are analyzed. The shear wave data processed can include dipole shear data (two-dimensional in shear) or dipole shear data plus Stoneley data (three-dimensional in shear).
However, performing conventional multi-dimensional analyses of shear data to determine formation properties may not provide accurate results.